Thanks Jon, I have been through the con/n con scenario.
The 568 is Controller and 5200 master is N controller.

When I get home I will re-configure everything and have the centre at the end of the chain again, with one of the 5200’s as master.

It’s been almost a month now, reading the manuals, replacing cables etc, that is why I think there’s a problem with the 568.

I have a few days off (instead of an hour here and there) so hopefully I will be able to work it out.

Thanks again

568.2, 5200’s, 5200hc, D1500 sub